Method of making masked lignocellulosic material



Jan 19, 1954 G. D. KING ETAL METHOD OF MAKING MASKED LIGNOCELLULOSICMATERIAL Filed April 21, 1951 l INVENTORS 'RUSSEL V. HARKEMA BYGLENGARRYD. KING ATTORNEY might otherwise be Patented Jan. 19, 1954 METHOD OFMAKING MASKED LIGNO- -CELLULOSIC MATERIAL Glengarry Russell V.

D. King, Washington, D. C., and Harkema, Seattle, Wash., assignors toCrown Zellerhach Corporation, San Francisco, Calif., a corporation ofNevada Application April 21, 1951, Serial N0. 222,264

1 Claim.

This invention relates in general to the manufacture of an improvedboard, the body of which is formed of forest material such as wood, orwoody or lignocellulosic fibers, and at least one face of which isrequired to be provided with a special masking. Y

More specifically this invention relates to an improved compositeproduct comprising an outer sheet of cellulosic material applied to andcombined with a board or base of woody material or lignocellulosicmaterial, particularly plywood.

The application of resin-containing paper to the face of plywood, in theform of what is known as plywood overlay, has recently come intoconsideration as a practical means of enabling poorer grades of plywoodto be employed. It has been known that resin-containing paper can bemade and bonded to plywood in order to provide an improved surfacingcapable, for example, of offering greater water-proofness or greaterresistance to abrasion or a more satisfactory surface for painting orsimilar treatment.

However, heretofore it has not been possible, even with heavyresin-containing overlay paper, entirely to cover up or mask surfaceirregularities, grain rise, or other natural but undesirable defects.Particularly is this true where patches or plugs are made in theplywood, this being customary procedure where knots or pitch pocketsoccur. Painting the surface of overlay may cover up discolorations ofthe underlying plywood surface, which would otherwise show through theoverlay, and paint will also generally cover any discoloring marks whichmay inadvertently be present in the overlay paper itself, but not evenpainting of the overlay will completely mask the surface irregularitiesin the plywood such as those above mentioned.

An object of the present invention is to provide an improved masking forsuch material as plywood, through the medium of which masking any andYall surface irregularities and all other undesirable characteristics,whichwould otherwise be apparent, will Ibe completely hidden orobliterated.

A related object of the invention is to provide an improved maskedproduct, as a component of which low-grade plywood, and plywood whichrejected, can be utilized.

Another and specific object of the invention is to provide an improvedmethod of overlaying" or masking plywood or other boardsoflignocellulosic material which` will produce a novel, attractive,durable and completely finished surface, entirely free from all trace ofany irregularities in the underlying plywood orbase.

A further object of the invention is to provide an improved maskedlignocellulosic board which can be advantageously employed in any of theuses for which plywood or plywood with an overlay can be employed.

A still further object of the invention is to provide an improved maskedboard which will be practical and inexpensive to produce, which willpossess a surface durability at least equal to any low density plywoodoverlay previously developed.

A difficulty heretoforev which has been encountered when a more or lessrigid sheet is applied to a comparatively rough, irregular or unevenplywood surface as an overlay is that there may not be a completebonding of the overlay and plywood inasmuch as the pressure exerted whenthe overlay is secured to the plywood is greatest on the high surfacespots and may result in bridging the high surface spots or insufficientbonding at the low surface spots. An additional object of the presentinvention is to prevent any such possibility by providing a strongpermanent bond between the plywood and overlay over every portion of thecovered surface regardless of surface irregularities.

Another object of the invention is to provide an improved unique maskedlignocellulosic board of the type above indicated which will affordopportunities for various decorative eiects.

The attainment of these objects and other advantages will be explainedin the course of the following description of our invention and of apreferred method of practicing the same.

Briey, in carrying out our invention with the masking of a plywoodsurface, we employ a resincontaining cellulosic sheet-for example heavypaper, treated with resin in such manner that the paper will remain hardsurfaced and tough throughout, and opaque to a considerable degreealthough nally subjected to a temperature higher than the curingtemperature of the resin. This sheet is bonded to the surface of theplywood, and then, either as part of the bonding operation or subsequentthereto; the sheet and covered plywood surface together are subjected toa heavy embossing treatment involving the simultaneous application ofembossing pressure and heat. The embossing treatment molds the surfaceto conform to the desired pattern presented by the embossing elementsand any previous surface irregularities are dispensedby the surfaceembossing molding. The temperature to which the surface is momentarilysubjected results in color effects in the resin-containing sheet, thenature or" which will be later explained. The final result is a hard,permanent resin-containing heavily embossed and irregularly coloredsurface, presenting an attractive finished appearance, the embossing andcoloring combining to provide a complete masking of the previous surfaceof the plywood, while the cured resin causes the composite finishedproduct to have a considerably tougher and harder surface than that ofthe plywood itself.

The resin-containing cellulosic sheet may be fabricated in several ways.The resin treatment should meet three requirements-namely, there 5should be a sufficient concentration or" the resin on the surface of thenal sheet to produce the necessary hard, tough, abrasion-resistingsurface; the body of the sheet must have and mustretain suiicient resinto prevent any delamination or splitting of the sheet within its center;and the total amount of resin used for treatment of the sheet should notbe so excessive as to render the sheet needlessly expensive. Also theresin and resin treatment employed should not be such as to reduce thedegree of opacity in the sheet.

One method oi producing such a resin-containing sheet involvestheapplication of resin at two intervals in the making of the sheet.Water insoluble resin is first introduced into the beater furnish andlater after calendering of the sheet further resin is applied in theform of a coating of water-soluble resin. Or the web, after leaving thepress rolls and preliminary driers, may be passed through a tankcontaining a solution of water-soluble resin and subsequently, after acalendering operation, the sheet is given a coating of water-solubleresin. Such applications of resin at two intervals in the making of asheet are described in U. S. Patent No. 2,497,712, issued February 14,1950, to R. J. Auchter, entitled Process of Manufacturing a FibrousSheet Covered Plywood.

While a sheet treated with resin according to the method of the abovementioned Patent No.

2,497,712 may be used in carrying out our invention, we prefer tointroduce the resin `only into the beater furnish. This can be donesatisfactorily by using a resin of the phenol-formaldehyde type andhaving the same precipiated on r and retained by the fibers. For thispurpose itis necessary that the resin be characterized by a highformaldehyde-phenol ratio with a sodium content of from 11/2% to 3% inthe mixture. The pH of the liquid resin should be from 8 to 9.5. Theresin is then precipitated on the fibers in the slurry by lowering thepH to 4 or 4.5 (this may be done, for example, by adding alum or amixture of alum and sulphuric acid, or by adding acetic acid orphosphoric acid). A resin which we have found very satisfactory to useis a resin manufactured by the Snyder Chemical Corporation of Bethel,Connecticut, under the designation Synoo 721. Another is a resinmanufactured by the American-Marietta Co. of Chicago, Illinois, andknown by the designation Amres 4971.

The further heating to which the sheet is subjected in the drierssolidies the resin but without curing it. A satisfactory sheet for thecarrying out of our invention may be composed of 85% standard chemicalor sulte pulp and 15% groundwocd pulp. Preferably the basis weight ofthe final sheet itself will be from oto 225 pounds per ream of 3000square feet and the amount QI resin content should be approximately 20%of this basis weight.

Assuming that our invention is to be employed in the masking of aplywood panel, the resincontaining sheet is glued to the race of thepanel by a conventional resin glue, preferably using approximately fivepounds or" resin glue per 1000 square feet. A resin glue satisfactorylor this purpose is a phenol-formaldehyde resin glue imanufactured bythe American-Marietta Co.

under the designation imres leO'.

The plywood panel and attached sheet are then placed in a heated pressand subjected to a pressure ofapproximately 260 pounds per square inchata temperature of approximately 300 F. and held under such pressure andtemperature for about seven minutes. This results in partial curing ofthe resin in the sheet and a curing of the resinglue. The coveredplywood surface is then ready for the nal step in our process.

The final step consists in subjecting the covered face or surface to aspecial embossing treatment. This may be accomplished by passing thepanel under a heated embossing roll. The embossing of course requiresgreater pressure than the 200 pounds per square inch employed inpressing the sheet to the wood face, and the pressure required willdepend to some extent upon the depth of the maximum indentations orstriations of the embossing pattern presented by the embossing roll. Thevalleys in the embossed pattern or design must be of sucient depth sothat any vprevious surface irregularities in the board will becompletely eliminated in the embossing 0r molding of the masked face.The depth oi the valleys will be at least equal to the thickness of 'themasking paper and, as illustrated in the drawings, will generally bedeeper than the thickness of the overlay paper.

The temperature under which the embossing is performed, that is to say,the surface heat of the embossing roll, is important. In the preferredform in which we carry out our invention, thus with the resin treatedsheet previously described, kwe have the surface temperature of theembossing roll approximately 600 F'. and pass the covered plywood underthe embossing roll at a speed of 30-35 feet per minute. This temperatureis ccnsiderably greater than the previous temperature (300 F.) to whichthe resin '1s subjected in the press, so that the resin softens topermit molding.

Such a temperature of 600 F. would be high enough to cause scorching ofthe paper sheet if the sheet had no excess resin. However, due to theresin on and in the sheet, no scorching occurs at this high temperatureof 600 F. at the speed (30 to 35 feet per minute) at which the sheet andunderlying panel pass under the embossing medium. 'One eiiect of theheat on the resin is to produce some discoloration of the resin vandthus of the sheet. This discoloration is greatest inthe valleys ordepressions on the embossed design, thus making a color contrast betweenridges and valleys in the finished embossed surface causing the embosseddesign to stand out more clearly and adding to the attractiveness orappearance of the surface of the final product.

In the accompanying drawings which illustrate the invention in part-Fig. 1 is an enlarged fragmentary cross-sectional view of a plywoodpanel with a resin-oontaining sheet secured on one face of the samepreparatory to the nal embossing;

Fig. 2 is -a corresponding cross-sectional View of the same panel afterthe embossing has'taken place;

Fig. 3 is a top planviewrof the embossed surface;

Fig. 4 is an enlarged fragmentary cross-sectional View of a similarplywood panel with both faces finished or masked in accordance with ourinvention; and

Fig. 5 is an enlarged fragmentary cross-sectional view of a compositefiber board having its faces finished in accordance with the invention.

In Figs. 1 and 2 the plywood panel comprises a core layer I!) with outeror veneer layers I i and panel is then passed under a heated embossing iroll causing ridges and valleys or striations y of a desired embossingkdesign, to be impressed into the masked sheet I3 and into the underlyingwood layer II.

The heat and pressure of the embossing roll Vnot only cause the resin toflow in the surface but also produce some discoloration or darkening ofthe resin in the sheet I3. The coloring in the valleys or striations ywill be darker than that of the ridges x due to the fact that the valleyor stria'tion portions have more and longer con-- tact with the heatedembossing roll and are subjected to greater heat and pressure than theridge portions. Thus-the contrast between the ridges and valleys will beintensified in appear- L ance, as indicated in Fig- 3, giving a verypleasing effect to the finished surface and producing a more completemasking of the original face of the plywood panel.

rThe extent of discoloration produced by the embossing will depend uponthe degree of the heat in the embossing roll or other embossing meansemployed, and of course care must be taken not to have the heat sointense that a burning of the resin and a corresponding scorching of theresin sheet would occur, as this would not only make the surface toodark but the masked sheet would then be brittle and not durable. For aless pronounced color effect the surface temperature of the embossingroll should be less than the suggested 600 F., but in any event must behigher than the temperature (300 F.) at which the initial and partialcuring of the resin was accomplished, otherwise the embossing mayproduce some cracks in the sheet along the ridges of the embossedsurface since the resin would not soften and be molded.

The speed at which the covered plywood passes under the embossing rolland the surface temperature of the embossing roli of course have animportant relationship. Thus if the speed were very much slower than thesuggested to 35 feet per minute, a surface temperature of 600 F. of theembossing roll could scorch the resin sheet, while if the speed wereconsiderably greater than 30 to 35 feet per minute a higher surfacetemperature than 600 F. not only would not scorch the sheet but would benecessary to produce a result comparable to the result obtained with thespeed and temperature suggested. The speed and temperature mentioned arementioned as a Vpreferred example because we' have found this tobepractical and very satisfactory. However, it is to be understood thatmany variations may be made within reason and satisfactory resultsobtained.

In many instances it is desirable to mask both faces of 'a plywood panelor other lignocellulosic product, and in such case a resin-containingsheet is secured to both faces of the panel and the rolls through whichthe panel is then ypassed are both embossing rolls and both are heatedto the samel desired surface temperature. Fig. 4 illustrates a plywoodpanel on which the masking of both faces is done similarly andsimultaneously.

While our invention probably has ing can of course be carried out withboards other than those of wood veneer. Fig. 5 illustrates a compositefiber board, both faces of which are masked in accordance with ourinvention. The masked surface is more durable, as well as moreattractive in appearance, than the ordinary surfaces of composite fiberboards.

Our invention could be carried out to a certain extent withmodifications. instead of a special Aresin-containing sheet, :ordinaryheavy kraft paper could be used for masking. In such case the paper issecured to the underlying surface similarly by a resin glue (preferablya phenolformaldehyde resin glue). While some of the resin from the gluewould then ,penetrate into the masking paper the amount, if any, ofresin which reached the outer face of the paper would be ini suflicientto produce a tough, durable surface which would generally be preferred.The Yresulting soft surface would produce good masking, but

the embossing could be done onlyl with a very moderate temperature andthe color; marking of the embossing would not be obtained.

Durable masking with a resin-containing sheet would of course bepossible With embossing and without any discoloration by dispensing withmost of the heat from the embossing rolls. However, such a mask wouldnot in extreme cases cover up all color marks in the underlying wood.For a complete and perfect masking surface we have found that both thecolor contrast in the embossing as Well as the changing of the surfacecontour by the embossing are necessary and desirable.

It would be possible in the carrying out of our invention, to eliminatethe placing of the panel and masking sheet first in a heated press forpartial curing of the resin prior to the final embossing. Thus, when themasking sheet has been attached to the panel with a layer of resin glue,the panel and sheet can be passed directly under the heated embossingroll. However, we consider that the more satisfactory procedure is torhave partial curing of the resin under a heated press take place priorto the embossing, since greater uniformity of the characteristics of thefinished surface will then be assured.

The embossing could of course be done with other means than embossingrolls, for example, by heated transfer molds or cauls. The use ofembossing rolls however we believe to be simpler and more practical. y

Although we prefer to use a phenol-formaldehyde resin for treating thepaper or cellulosic sheet, our invention can also be carried out withurea-formaldehyde resin. For example, we have used paper made from apulp furnish of '70% sulfite and 30% groundwood and treated withurea-formaldehyde resin. The particular urea- K its greatestl utility inthe masking of plywood, asimilar maskassuma 7 formaldehydel resin whichwe have used for this purpose isA made by' Hercules Powder Company ofWilmington, Delaware, andi is known under thev trade name of Hercules138;.' We added this urea-formaldehyde resin tothe pulp `iurnish in thebeater, allowing 15 pounds of the resin for each 85 pounds ofA pulp.Sufficient alum was addedV to lower the pH to 4.5. A paper sheetweighing 200 pounds per ream totaling 3000 square feet was formed anddried in the conventional manner. The dried resin-containing paper wasglued to the surface of plywood to be masked. We usedphenol-formaldehyde glue, allowing five pounds of glue per 1000 squarefeet. The covered plywood was placed in a heated platenpress and pressedat approximately 200 pounds per square inch and at a surface temperatureof 300 F. for about 7 minutes, thus in the same manner as previouslydescribed `for a phenol-formaldehyde resin-containing paper,

and. the covered plywood, panel was then ernbossed also in the samemanner.

The resulting embossed surface, when the urea-formaldehyde resin is thusused. for treating the paper, will be found to be lighter in color thanwhen paper treated with phenolformaldehyde resin is employed. Butwhile-the embossed final product presents a surface having a hardnesssimilar to that attained with the paper treated withphenol-formaldehyde' resin, the surface does not have the same waterresistance. 'Thus we have found that the use of urea-formaldehyde resinfor treating the paper in the carrying out of ourl invention does notproduce a product which would have sufiicient Weather resistance to beentirely satisfactory for use out-of-doors.

We claim: l

The method of manufacturing an .improved masked board, which methodcomprises covering a face of a plywood panel with a sheet of papertreated with a phenol-formaldehyde resin, the amount of said resin insaid sheet being not less than approximately' 20% of the weight of thefinished sheet, the resin having been precipitated onV the bers'in thesheet in the making of the sheet, using a phenol-formaldehyde resin gluefor attaching said sheet to said face of said plywood panel, placingsaid plywood panel in a heated press under a pressure of approximately200 pounds per square inch at a temperature of approximately 300 F. forabout l minutes in order to ele'ct partial curing of the in said sheetand a curing of the resin in glue, andA molding said covered plywoodpanel face into a design pattern by passing the same under a heatedembossing roll having a surface heat of approximately 600 F. at a speedci 30 to 35 feet per minute and under pressure of at least 400 poundsper square inch, whereby the resin in the Valleys in said molded designwill darker in color than the ridges in said design without causing ascorching of said sheet, and thereby providing a better masking for saidplywood face.

GLEN GARRY D. IING. RUSSELL V. HARKEMA.

References Cited in the iile of this patent UNITED STATES PATENTS NumberName Date 1,852,964 George Apr. 5, 1932 1,999,383 Woodall Apr. 30, 19352,086,187 Norton July 6, 1937 2,137,238 Collins Nov. 22, 1938 2,219,251Catini Oct. 22, 1940 2,245,169 Von Ende June 10, 1941 2,343,740Birmingham Mar. '1, 1944 2,442,422 Loetscher June 1, 1948

